Our invention relates to a method of writing on a magnetic recording tape without the danger of accidental overwriting, that is, of accidentally destroying prewritten information on the tape. The writing method of our invention has particular utility in conjunction with digital multitrack recording tapes, although we do not wish our invention to be limited to this specific application.
Digital multitrack recording tapes packaged in cassette or cartridge form have found widespread acceptance as compact, high capacity storages of computer information. Such a tape has a plurality or multiplicity of parallel record tracks extending longitudinally of the tape. U.S. Pat. No. 4,422,111 to Moeller et al. discloses an example of recorder for use with a multitrack tape. The recorder has a record/playback head movable from track to track across the width of the tape. A bidirectional stepper motor is normally employed in combination with a suitable motion translating mechanism for such head travel.
As is well known, the stepper motor rotates in short, discrete steps in response to drive pulses. Each drive pulse determines each discrete angle of rotation of the stepper motor and, in consequence, each step of head travel across the width of the multitrack tape. Therefore, first placed in a transverse reference position proximate one edge of the tape, the head can be stepped to a desired track location on the tape by impressing a required number of drive pulses to the motor. The stepper motor represents one of the most efficient, inexpensive head positioning means.
Occasionally, however, the stepper motor or the motion translating mechanism may malfunction, as all man made machines will, failing to position the head in a desired track location on the tape. Assume that the head is positioned on some wrong track, and that information has already been written on this track. If then information is overwritten on the wrong track, the prewritten information will be destroyed.
The same problem can occur not only in recording computer information but also audio signals. Both the tape cassette for the storage of computer information and the digital audio tape cassette are conventionally provided with a file protect tab on the cassette housing. A removal of this tab makes it impossible to record on the tape. However, the user will not break off the file protect tab if he intends the cassette for additional recording. The file protect tab is therefore not reliable in this case for the protection of prerecorded information.